1. Field of the Invention
This invention relates to safety devices and particularly to devices for preventing the accidental release of the parking brake valves of motor vehicles, especially school buses and commercial buses, trucks and tractor-trailer combinations. The devices incorporate the conventional push-pull switch assemblies found on the dashboards of such vehicles, but are modified to include means for avoiding inadvertent disengagement of the brakes of the vehicles.
2. Brief Description of the Prior Art
In many motor vehicles, especially school buses and commercial buses, truck and tractor-trailer systems, air braking systems are used. Typically, the parking brake in such a system is set, i.e. the brakes are engaged, by the operator's actuating a dashboard mounted push-pull switch which controls the operation of the valves in the system. The switch assembly for operating the parking brake is mounted on the dashboard in clear view of the vehicle operator and those persons seated in the areas adjacent the operator's seat. A knob on the switch assembly also normally carries information adjacent the switch indicating the control positions of the switch, for example, "Push to Release" and "Pull to Apply" the parking brake.
The easy accessibility of the switch assembly for the brake valve which controls the only parking brake on most of those commercial vehicles creates a dangerous situation in that children or adults can accidentally actuate the switch assembly, thus releasing the parking brakes. In addition, the attractiveness of the switch assembly knob to curious children and adults makes the situation undesirable.
The operation of the parking brake system on large vehicles, such as buses and trucks, is controlled by air and springs. When air pressure is relieved, the brakes on the vehicles are applied by spring loaded canisters mounted near the rear wheels which apply the wheel brakes by rotating a cam which presses the brake lining against the brake drums. When the air pressure is increased to 60 psi and 120 psi, the switch assembly knob on the dashboard can be pushed in to release air to the canisters which, in turn, reverses the action and releases the brakes.
When the vehicle is operated, the air pressure generally ranges between 90 and 120 pounds. When the vehicle is not being moved, however, and is parked, and the air pressure is 60 pounds or greater, the danger of accidental release of the parking brake is greatest since anyone or anything can bump the parking brake switch assembly with very little effort, push in the parking brake knob and release the brakes, causing the vehicles to move. By the present invention, this free wheeling through accidental release of the parking brake can be prevented.